SYSTEM AND METHOD FOR QoS-BASED STORAGE TIERING AND MIGRATION TECHNIQUE

ABSTRACT

The present invention is directed to a method for providing Quality Of Service (QoS)-based storage tiering and migration in a storage system. The method allows for configurable application data latency thresholds to be set on a per user basis and/or a per application basis so that a storage tiering mechanism and/or a storage migrating mechanism may be triggered for moving application data to a different class of storage.

FIELD OF THE INVENTION

The present invention relates to the field of storage resource and datamanagement and particularly to a system and method for Quality ofService (QoS)-based storage tiering and migration technique.

BACKGROUND OF THE INVENTION

Currently available methods for providing storage resource and datamanagement in data storage systems may not provide a desired level ofperformance.

Therefore, it may be desirable to provide system(s) and method(s) forproviding storage resource and data management in a data storage systemwhich addresses the above-referenced shortcomings of currently availablesolutions.

SUMMARY OF THE INVENTION

Accordingly, an embodiment of the present invention is directed to amethod for providing Quality Of Service (QoS)-based storage tiering andmigration in a storage system, said method including the steps of:monitoring an application process when the application process isaccessing a first storage tier of the storage system; based on saidmonitoring, determining a QoS factor measurement of the applicationprocess; comparing the QoS factor measurement to at least one of: afirst pre-determined QoS factor threshold (ex.—a tier threshold) and asecond pre-determined QoS factor threshold (ex.—a migrate threshold);when said comparing indicates that the QoS factor measurement is greaterthan the first pre-determined QoS factor threshold, creating aPoint-in-Time (PiT) copy and establishing an access permission of thePiT copy as Read Only, wherein the PiT copy is based upon the firststorage tier; when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and greater than the second pre-determined QoS factor threshold,migrating data from the PiT copy to a second storage tier; after themigrating of data from the PiT copy to the second storage tier hascompleted, setting establishing access permissions of the second storagetier as Read and Write and directing I/O commands to the second storagetier; when said comparing indicates that the QoS factor measurement is:less than the first pre-determined QoS factor threshold; and less thanthe second pre-determined QoS factor threshold, mirroring second storagetier data to the first storage tier; when mirroring of data of thesecond storage tier data to the first storage tier is synchronized,directing read commands to the second storage tier; when mirroring ofthe second storage tier data to the first storage tier is synchronized,synchronizing write commands between the first storage tier and thesecond storage tier.

A further embodiment of the present invention is directed to a computerprogram product comprising: a signal bearing medium bearing:computer-usable code configured for monitoring an application processwhen the application process is accessing a first storage tier of thestorage system; computer-usable code configured for based on saidmonitoring, determining a QoS factor measurement of the applicationprocess; computer-usable code configured for comparing the QoS factormeasurement to at least one of: a first pre-determined QoS factorthreshold and a second pre-determined QoS factor threshold;computer-usable code configured for, when said comparing indicates thatthe QoS factor measurement is greater than the first pre-determined QoSfactor threshold, creating a Point-in-Time (PiT) copy and establishingan access permission of the PiT copy as Read Only, wherein the PiT copyis based upon the first storage tier; computer-usable code configuredfor, when said comparing indicates that the QoS factor measurement is:less than the first pre-determined QoS factor threshold; and greaterthan the second pre-determined QoS factor threshold, migrating data fromthe PiT copy to a second storage tier; computer-usable code configuredfor, after the migrating of data from the PiT copy to the second storagetier has completed, setting establishing access permissions of thesecond storage tier as Read and Write and directing I/O commands to thesecond storage tier; computer-usable code configured for, when saidcomparing indicates that the QoS factor measurement is: less than thefirst pre-determined QoS factor threshold; and less than the secondpre-determined QoS factor threshold, mirroring second storage tier datato the first storage tier; computer-usable code configured for, whenminoring of data of the second storage tier data to the first storagetier is synchronized, directing read commands to the second storagetier; computer-usable code configured for, when mirroring of the secondstorage tier data to the first storage tier is synchronized,synchronizing write commands between the first storage tier and thesecond storage tier.

A still further embodiment of the present invention is directed to astorage system, including: a processor; a memory, said memory beingconnected to the processor; and control programming for executing on theprocessor, wherein the control programming is configured for: monitoringan application process when the application process is accessing a firststorage tier of the storage system; based on said monitoring,determining a QoS factor measurement of the application process;comparing the QoS factor measurement to at least one of: a firstpre-determined QoS factor threshold and a second pre-determined QoSfactor threshold; and when said comparing indicates that the QoS factormeasurement is greater than the first pre-determined QoS factorthreshold, creating a Point-in-Time (PiT) copy and establishing anaccess permission of the PiT copy as Read Only, wherein the PiT copy isbased upon the first storage tier, wherein said control programming isfurther configured for: when said comparing indicates that the QoSfactor measurement is: less than the first pre-determined QoS factorthreshold; and greater than the second pre-determined QoS factorthreshold, migrating data from the PiT copy to a second storage tier;after the migrating of data from the PiT copy to the second storage tierhas completed, setting establishing access permissions of the secondstorage tier as Read and Write and directing I/O commands to the secondstorage tier; when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and less than the second pre-determined QoS factor threshold, mirroringsecond storage tier data to the first storage tier; when mirroring ofdata of the second storage tier data to the first storage tier issynchronized, directing read commands to the second storage tier; whenminoring of the second storage tier data to the first storage tier issynchronized, synchronizing write commands between the first storagetier and the second storage tier.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the present invention may be betterunderstood by those skilled in the art by reference to the accompanyingfigures in which:

FIG. 1A is a block diagram illustration of a plurality of applicationprocesses accessing a storage pool of a storage system of the presentinvention at a time when QoS factors associated with the applicationprocesses are at an optimum level during runtime in accordance with anexemplary embodiment of the present invention;

FIG. 1B is a block diagram illustration of a plurality of applicationprocesses accessing a storage pool of a storage system of the presentinvention at a time when a QoS factor associated with one of theapplication processes has degraded in accordance with an exemplaryembodiment of the present invention;

FIG. 2 is a graphical representation illustrating a QoS factormeasurement plotted against sampling time, along with tier threshold andmigrate threshold trigger point settings for an exemplary storage systemof the present invention in accordance with an exemplary embodiment ofthe present invention;

FIG. 3A is a block diagram illustration of activity (ex.—data flow)within a storage system of the present invention when comparison of theQoS factor measurement to the Tier Threshold (TTH) indicates that theQoS factor measurement is greater than the TTH, in accordance with anexemplary embodiment of the present invention;

FIG. 3B is a block diagram illustration of migrating of data within astorage system of the present invention which may occur when comparisonof the QoS factor measurement to the Tier Threshold (TTH) and theMigrate Threshold (MTH) indicates that the QoS factor measurement isless than the TTH, but greater than the MTH, in accordance with anexemplary embodiment of the present invention;

FIG. 3C is a block diagram illustration of mirroring of data within astorage system of the present invention which may occur when comparisonof the QoS factor measurement to the Tier Threshold (TTH) and theMigrate Threshold (MTH) indicates that the QoS factor measurement isless than the TTH and less than the MTH; and

FIG. 4 depicts a flow chart illustrating a method for providing Qualityof Service (QoS)-based storage tiering and migration in a storage systemin accordance with a further exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the presently preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

A number of current commercially available storage tiering mechanismsmay be based upon the following: 1) cost per byte of storage space; 2)data access patterns; and 3) migration and placement of less frequentlyaccessed data to a lower class storage device. However, none of thesecurrent commercially available storage tiering mechanisms address thequality aspects pertaining to the data that a user is accessing on aday-to-day basis. Further, in these current commercially availablestorage tiering mechanisms no configurable Quality Of Service (QoS)parameters (Note: Quality of Service may also be abbreviated as (QoS))are available to set the data access latency thresholds for triggeringthe tiering/migrating process based on application process and userdata.

The system(s) and method(s) of the present invention, such as thosedisclosed herein, allow for configurable application data latencythresholds to be set on a per user basis and/or on a per applicationbasis, such that a storage tiering mechanism (ex.—a storage migratingmechanism) is triggered for moving application data to a different classof storage. Further, the system(s) and method(s) of the presentinvention, such as those disclosed herein, may further provide thefollowing features: 1) promoting of significant improvement in QoSlevels associated with applications hosted by a storage subsystem; 2)predictable latency associated with storage access; 3) tunability, forensuring complete utilization of storage resources which deliver thehighest QoS, thereby delivering a full Return On Investment (ROI) onhigh performance tiers; 4) on-the-fly manual administration forimproving QoS for business critical and/or time critical applicationneeds; 5) automatic retiring of lower performing storage based upon QoSthresholds; 6) automatic migration of user and application data to adifferent storage tier based on QoS thresholds; 7) significantimprovements in sustaining predictable application performance on sharedstorage; 8) significant improvement in latency associated withapplication specific data access; 9) automatic policy-based tiering andmigration without requiring human intervention; and 10) predictivemodeling and projections to recommend needed capacity of highperformance tiers and lower performing tiers based on historical use.Further, the system(s) and method(s) of the present invention, such asthose disclosed herein, may involve changing enterprise levelconfigurable QoS parameters on a per user, per application basis by anadministrator. Still further, the system(s) and method(s) of the presentinvention provide for spontaneous storage tiering and migration based ona QoS concept applied at a user level and/or an application data level.

Referring generally to FIGS. 1A, 1B and 3A through 3C, a storage system100 upon/within which the method(s) for providing Quality of Service(QoS)-based storage tiering and migration may be implemented is shown inaccordance with exemplary embodiments of the present invention. Inexemplary embodiments, the storage system 100 may include a processor102. In further embodiments, the storage system 100 may further includea memory 104 (ex.—Random Access Memory (RAM)). In still furtherembodiments, the storage system 100 may further include a bus 106. Forinstance, the processor 102 and the memory 104 may be connected to thebus 106. In current embodiments of the present invention, the storagesystem 100 may include a storage subsystem, which may further include aplurality of storage tiers, such as a first storage tier 108 and asecond storage tier 112. Each storage tier may include one or morestorage devices which make up a storage pool (ex.—a base volume 108) forthat storage tier. Further, the first storage tier may be a differentclass of storage than the second storage tier, the two storage tiersbeing distinguished by the performance of the storage devices belongingto the first tier compared to the performance of the storage devicesbelonging to the second tier (ex.—one tier's storage devices may behigher performing storage devices than the storage devices of the othertier). In further embodiments of the present invention, the storagesubsystem of the storage system 100 may be connected to the processor102 and the memory 104 via the bus 106. In still further embodiments ofthe present invention, the system 100 may be configured (ex—via controlprogramming executing on the processor 102) for allowing method(s) forproviding Quality Of Service (QoS)-based storage tiering and migrationto be performed via and/or within the storage system 100, as will be setforth below.

Referring to FIG. 4, a flowchart is provided which illustrates a methodfor providing Quality of Service (QoS)-based storage tiering andmigration in a storage system, in accordance with an exemplaryembodiment of the present invention. The method 400 may include the stepof: monitoring an application process when the application process isaccessing a first storage tier of the storage system 402. For example,in the storage system 100 of the present invention, one or more QoSfactors 160 of/corresponding to one or more application processes 150may be monitored (ex.—continuously monitored and/or sampled) as theapplication processes are accessing a storage pool (ex.—a base volume108) of a first storage tier (as shown in FIGS. 1A and 1B). In exemplaryembodiments of the present invention, the QoS factors 160 may bereal-time QoS factors associated with/pertaining to/corresponding to theapplication processes 150. FIG. 1A illustrates a plurality ofapplication processes 150 accessing the storage pool 108 of the firststorage tier when QoS factors 160 are at an optimum level duringruntime. Monitoring (ex.—sampling) may be done in real-time in order tokeep the monitoring window open for as long as the application processes150 are active. In current embodiments of the present invention, some ofthe QoS factors 160 which may govern the application processes 150 inreal-time may include but are not limited to the following: readlatency; write latency; storage media response time; idle time (ex.—timewhen no active reads/writes are performed); pervasiveness of data(ex.—data being written and read are in close proximity within anapplication share hosted in a storage device of the storage subsystem);data localization (ex.—degree to which particular data location(s) arebeing accessed compared to others); age of data; and age of applicationfiles.

In further embodiments, the method 400 may further include, based uponsaid monitoring, determining a QoS factor measurement of the applicationprocess 404. For instance, when QoS factor(s) 160 of (ex.—associatedwith) application processes 150 are being monitored, reading(s) ormeasurement(s) for the QoS factor(s) may be determined. Thesemeasurements (ex.—QoS factor measurements) may be continuouslydetermined for the duration of monitoring. After a period of time, oneor more QoS factor(s) 160 associated with a particular applicationprocess 150 may begin to deteriorate (as shown via the designation“Critical QoS” in FIG. 1B), thereby impacting overall QoS thresholds forthat particular application process. In exemplary embodiments of thepresent invention, the method 400 may further include the step of:comparing the QoS factor measurement to at least one of: a firstpre-determined QoS threshold (ex.—a Tier Threshold (TTH)) and a secondpre-determined QoS factor threshold (ex.—a Migrate Threshold (MH)) 406.In current embodiments, these thresholds may serve as trigger points forlatency aspects of the system 100. For example, based upon saidcomparison, the Tier Threshold and the Migrate Threshold may serve astrigger points which may trigger the system 100 to execute a sequence ofsteps for: a) storage tiering; or b) migrating application data to adifferent class of storage respectively, as will be described in furtherdetail below. The graphical representation (ex.—graph) 200 shown in FIG.2 illustrates a QoS level(s)/a measurement of a QoS factor (ex.—storagelatency associated with application data) plotted against sampling time(ex.—monitoring time). A first region of the graph 202 illustrates apoint in time when the application processes 150 are running at optimumQoS levels. Solid line 204 indicates actual non-tiered storage latency.Dashed line 206 indicates predicted non-tiered storage latency. Dottedline 208 indicates actual latency measured after application data istiered to a different class (ex.—tier) of storage. Within the samplingperiod (SP), the QoS levels may be measured and compared against thetrigger thresholds (ex.—the Tier Threshold (TTH) and the MigrateThreshold (MTH).

In exemplary embodiments of the present invention, the method 400 mayfurther include, when said comparing indicates that the QoS factormeasurement is greater than the first pre-determined QoS factorthreshold, creating a Point-in-Time (PiT) copy and establishing anaccess permission of the PiT copy as Read Only, wherein the PiT copy isbased upon the first storage tier 408. For example, as shown in FIG. 3A,when the comparison of the QoS factor measurement to the Tier Threshold(TTH) indicates that the QoS factor measurement is greater than the TTH,one or more PiT copies 110 (ex.—PiT snapshots or PiTs) may be createdbased upon the first storage tier (ex.—may be created off of the basevolume 108).

In further embodiments of the present invention, the method 400 mayfurther include migrating data from the PiT copy to a second storagetier when said comparing indicates that the QoS factor measurement is:less than the first pre-determined QoS factor threshold; and greaterthan the second pre-determined QoS factor threshold 410. For instance,as shown in FIG. 3B, when the comparison of the QoS factor measurementto the Tier Threshold (TTH) and the Migrate Threshold (MTH) indicatesthat the QoS factor measurement is less than the TTH, but greater thanthe MTH, data may be migrated from the one or more PiT copies (ex.—PiTs)110 to a second (ex.—next) storage tier 112. A heuristic approach may beimplemented when migrating said data for promoting prevention ofthrashing in cases when the QoS factor measurement(s) (ex.—the QoS) mayfluctuate quickly between thresholds.

In current embodiments of the present invention, the method 400 mayfurther include, after the migrating of data from the PiT copy to thesecond storage tier has completed, setting establishing accesspermissions of the second storage tier as Read and Write and directingI/O commands to the second storage tier 412. For example, once all thedata from the one or more PiT copies 110 has been migrated to the secondstorage tier 412, incoming I/Os may be re-directed to and serviced bythe second storage tier 112, with the access permissions of the secondstorage tier 112 being set to Read and Write (R/W) and PiT copies beingcontinuously generated off of the base volume 108.

In exemplary embodiments of the present invention, the method 400 mayfurther include, when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and less than the second pre-determined QoS factor threshold, mirroringsecond storage tier data to the first storage tier 414. For instance, asshown in FIG. 3C, when the comparison of the QoS factor measurement tothe Tier Threshold (TTH) and the Migrate Threshold (MTH) indicates thatthe QoS factor measurement is less than the TTH and less than the MTH,data in the second storage tier 112 may be mirrored to the first storagetier 108. A heuristic approach may be implemented when mirroring saiddata in order to prevent thrashing between thresholds.

In further embodiments of the present invention, the method 400 mayfurther include, when mirroring of data of the second storage tier datato the first storage tier is synchronized, directing read commands tothe second storage tier 416 and synchronizing write commands between thefirst storage tier and the second storage tier 418. For example, whenmirroring (ex.—mirror) is synchronized, all reads may be serviced by thesecond tier 112 and all writes may be synchronized between the basevolume 108 and the second tier 112.

It is to be noted that the foregoing described embodiments according tothe present invention may be conveniently implemented using conventionalgeneral purpose digital computers programmed according to the teachingsof the present specification, as will be apparent to those skilled inthe computer art. Appropriate software coding may readily be prepared byskilled programmers based on the teachings of the present disclosure, aswill be apparent to those skilled in the software art.

It is to be understood that the present invention may be convenientlyimplemented in forms of a software package. Such a software package maybe a computer program product which employs a computer-readable storagemedium including stored computer code which is used to program acomputer to perform the disclosed function and process of the presentinvention. The computer-readable medium/computer-readable storage mediummay include, but is not limited to, any type of conventional floppydisk, optical disk, CD-ROM, magnetic disk, hard disk drive,magneto-optical disk, ROM, RAM, EPROM, EEPROM, magnetic or optical card,or any other suitable media for storing electronic instructions.

It is understood that the specific order or hierarchy of steps in theforegoing disclosed methods are examples of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the method can be rearranged while remainingwithin the scope of the present invention. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

It is believed that the present invention and many of its attendantadvantages will be understood by the foregoing description. It is alsobelieved that it will be apparent that various changes may be made inthe form, construction and arrangement of the components thereof withoutdeparting from the scope and spirit of the invention or withoutsacrificing all of its material advantages. The form herein beforedescribed being merely an explanatory embodiment thereof, it is theintention of the following claims to encompass and include such changes.

1. A method for providing Quality of Service (QoS)-based storage tieringand migration in a storage system, said method comprising: monitoring anapplication process when the application process is accessing a firststorage tier of the storage system; based on said monitoring,determining a QoS factor measurement of the application process;comparing the QoS factor measurement to at least one of: a firstpre-determined QoS factor threshold and a second pre-determined QoSfactor threshold; and when said comparing indicates that the QoS factormeasurement is greater than the first pre-determined QoS factorthreshold, creating a Point-in-Time (PiT) copy and establishing anaccess permission of the PiT copy as Read Only, wherein the PiT copy isbased upon the first storage tier.
 2. A method as claimed in claim 1,further comprising: when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and greater than the second pre-determined QoS factor threshold,migrating data from the PiT copy to a second storage tier.
 3. A methodas claimed in claim 2, further comprising: after the migrating of datafrom the PiT copy to the second storage tier has completed, settingestablishing access permissions of the second storage tier as Read andWrite and directing I/O commands to the second storage tier.
 4. A methodas claimed in claim 3, further comprising: when said comparing indicatesthat the QoS factor measurement is: less than the first pre-determinedQoS factor threshold; and less than the second pre-determined QoS factorthreshold, mirroring second storage tier data to the first storage tier.5. A method as claimed in claim 4, further comprising: when mirroring ofdata of the second storage tier data to the first storage tier issynchronized, directing read commands to the second storage tier.
 6. Amethod as claimed in claim 5, further comprising: when mirroring of thesecond storage tier data to the first storage tier is synchronized,synchronizing write commands between the first storage tier and thesecond storage tier.
 7. A method as claimed in claim 1, wherein the QoSfactor measurement is based upon a QoS factor of the storage system,said QoS factor being at least one of: read latency; write latency;storage media response time; idle time; data pervasiveness; datalocalization; age of data; and age of application files.
 8. A method asclaimed in claim 1, wherein the first pre-determined QoS factorthreshold is a tier threshold and the second pre-determined QoS factorthreshold is a migrate threshold.
 9. A computer program productcomprising: a signal bearing medium bearing: computer-usable codeconfigured for monitoring an application process when the applicationprocess is accessing a first storage tier of a storage system;computer-usable code configured for, based on said monitoring,determining a QoS factor measurement of the application process;computer-usable code configured for comparing the QoS factor measurementto at least one of: a first pre-determined QoS factor threshold and asecond pre-determined QoS factor threshold; and computer-usable codeconfigured for, when said comparing indicates that the QoS factormeasurement is greater than the first pre-determined QoS factorthreshold, creating a Point-in-Time (PiT) copy and establishing anaccess permission of the PiT copy as Read Only, wherein the PiT copy isbased upon the first storage tier.
 10. A computer program product asclaimed in claim 9, the signal-bearing medium further bearing:computer-usable code configured for, when said comparing indicates thatthe QoS factor measurement is: less than the first pre-determined QoSfactor threshold; and greater than the second pre-determined QoS factorthreshold, migrating data from the PiT copy to a second storage tier.11. A computer program product as claimed in claim 10, thesignal-bearing medium further bearing: computer-usable code configuredfor, after the migrating of data from the PiT copy to the second storagetier has completed, setting establishing access permissions of thesecond storage tier as Read and Write and directing I/O commands to thesecond storage tier.
 12. A computer program product as claimed in claim11, the signal-bearing medium further bearing: computer-usable codeconfigured for, when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and less than the second pre-determined QoS factor threshold, mirroringsecond storage tier data to the first storage tier.
 13. A computerprogram product as claimed in claim 12, the signal-bearing mediumfurther bearing: computer-usable code configured for, when mirroring ofdata of the second storage tier data to the first storage tier issynchronized, directing read commands to the second storage tier.
 14. Acomputer program product as claimed in claim 13, the signal-bearingmedium further bearing: computer-usable code configured for, whenmirroring of the second storage tier data to the first storage tier issynchronized, synchronizing write commands between the first storagetier and the second storage tier.
 15. A computer program product asclaimed in claim 9, wherein the QoS factor measurement is based upon aQoS factor of the storage system, said QoS factor being at least one of:read latency; write latency; storage media response time; idle time;data pervasiveness; data localization; age of data; and age ofapplication files.
 16. A computer program product as claimed in claim 9,wherein the first pre-determined QoS factor threshold is a tierthreshold and the second pre-determined QoS factor threshold is amigrate threshold.
 17. A storage system, comprising: a processor; amemory, said memory being connected to the processor; and controlprogramming for executing on the processor, wherein the controlprogramming is configured for: monitoring an application process whenthe application process is accessing a first storage tier of the storagesystem; based on said monitoring, determining a QoS factor measurementof the application process; comparing the QoS factor measurement to atleast one of: a first pre-determined QoS factor threshold and a secondpre-determined QoS factor threshold; and when said comparing indicatesthat the QoS factor measurement is greater than the first pre-determinedQoS factor threshold, creating a Point-in-Time (PiT) copy andestablishing an access permission of the PiT copy as Read Only, whereinthe PiT copy is based upon the first storage tier.
 18. A storage systemas claimed in claim 17, wherein said control programming is furtherconfigured for: when said comparing indicates that the QoS factormeasurement is: less than the first pre-determined QoS factor threshold;and greater than the second pre-determined QoS factor threshold,migrating data from the PiT copy to a second storage tier; after themigrating of data from the PiT copy to the second storage tier hascompleted, setting establishing access permissions of the second storagetier as Read and Write and directing I/O commands to the second storagetier; when said comparing indicates that the QoS factor measurement is:less than the first pre-determined QoS factor threshold; and less thanthe second pre-determined QoS factor threshold, mirroring second storagetier data to the first storage tier; when mirroring of data of thesecond storage tier data to the first storage tier is synchronized,directing read commands to the second storage tier; when mirroring ofthe second storage tier data to the first storage tier is synchronized,synchronizing write commands between the first storage tier and thesecond storage tier.
 19. A storage system as claimed in claim 17,wherein the QoS factor measurement is based upon a QoS factor of thestorage system, said QoS factor being at least one of: read latency;write latency; storage media response time; idle time; datapervasiveness; data localization; age of data; and age of applicationfiles.
 20. A storage system as claimed in claim 17, wherein the firstpre-determined QoS factor threshold is a tier threshold and the secondpre-determined QoS factor threshold is a migrate threshold.